1. Field of the Invention
The present invention relates to an inverter circuit and, more particularly, to an inverter circuit which controls discharge tubes of a plurality of cold cathode fluorescent lamps (“CCFLs”) of a liquid crystal display (“LCD”), a backlight device having the inverter circuit and an LCD having the backlight device.
2. Description of the Related Art
A liquid crystal display (“LCD”) is a common type of display apparatus. The LCD is not a self-emissive display apparatus, however, and therefore requires a separate light source, such as a cold cathode fluorescent lamp (“CCFL”), for example.
The CCFL is a type of a fluorescent lamp. Compared to other lamp types, such as a heat cathode fluorescent lamp (“HCFL”), for example, the CCFL is highly resistant to vibration, has a relatively small diameter and has a long lifespan. However, a higher driving voltage must be applied to the CCFL than to the HCFL, since the CCFL is turned on and off in response to a high AC voltage.
Due to the high AC voltage, an abnormal discharge, such as a corona discharge or an arc discharge, for example, may occur between a high voltage section and a ground in an inverter circuit which generates the high AC voltage to operate the CCFL. The abnormal discharge carbonizes a peripheral section of the CCFL and also causes additional problems, such as short-circuits, fires and smoking during operation.
FIG. 1 is a block diagram of a backlight device of the prior art. Referring to FIG. 1, a backlight device 1 of the prior art includes an inverter circuit 2 which generates a high AC voltage, a CCFL group 3 having a plurality of CCFLs, and a condenser circuit 4 having a plurality of balance condensers BC which uniformly distributes the high AC voltage from the inverter circuit 2 to the plurality of CCFLs.
The inverter circuit 2 of the backlight device 1 of the prior art is typically a concentrative power supply-type inverter circuit 2 which turns on and off CCFLs of the plurality of CCFLs. The inverter circuit 2 also prevents electric current from being concentrated in a particular CCFL, such as in a CCFL which turns on before other CCFLs due to a negative resistance characteristic of that particular CCFL, for example. Specifically, the inverter circuit 2 prevents the electric current from being concentrated in a particular CCFL by connecting a corresponding balance condenser BC the CCFL having the negative resistance characteristic.
In the backlight device 1 having the concentrative power supply-type inverter circuit 2, however, an arc discharge occurs around the CCFLs. A current applied to the CCFLs is limited by the balance condensers, however, and an output current Io of the inverter circuit 2 is therefore not substantially affected by the arc discharge. Thus, the inverter circuit 2 is unable to detect the arc discharge detected based on the output current Io.
FIG. 2A is a graph of an output current of the inverter circuit of the prior art when arc discharge is not occurring, e.g., in a normal operating state, and FIG. 2B is a graph of an output current of the inverter circuit of the prior art when an arc discharge is occurring.
As shown in FIGS. 2A and 2B, a change in respective output waveforms of the output current Io due to the occurrence of an arc discharge is small, and the arc discharge is therefore not easy to detect. However, it is required to detect the arc discharge to block a power supply operation of the inverter circuit, since the arc discharge damages the CCFLs. Thus, it is desired to develop an inverter circuit capable of detecting an arc discharge to block a power supply operation, thereby effectively preventing damage to the CCFLs.